I found this on Answers.com
---------------------------------
Does peanut butter go bad?
It can, but it would have to have some contaminate added. Peanut butter has a natural bacteria fighter in it that keeps it from spoiling. The only thing that happens is it may seperate, the jar will look like an oily paint. Thats all you need to do is stir it. Peanut butter has a very long shelf life.